A Basic Text-Based Recording Studio

Shrinkwrapped audio gear too expensive? Too inflexible? Perhaps not geeky enough? Why not use a Linux box as the main workhorse in your studio?

Whether you're into Metal, Jazz, Noise, Baroque or something in between,
it is becoming more and more popular for artists to take on not only
the roles of composer and performer, but also the roles of audio engineer,
producer and even distributor of their own work.

The capability and quality of Linux audio applications are very good
and constantly improving. Support for high-end and low-end audio cards
is also getting better all the time. Whether it becomes the dominant
platform in the field is largely irrelevant—those of us who
find the flexibility of Linux and open-source tools to be valuable now
have a platform suitable for creating high-quality audio tracks.

This article outlines a simple method, which may be built upon, for
recording layered, multitrack recordings. In keeping with the Linux
tradition, in this article, we discuss a number of small, command-line tools that
perform very specific tasks very well. We then combine the power of
each of these tools into a digital audio workstation. As you will see,
using these tools in such a way, it is possible to overcome the (rare)
shortcomings in some of these tools.

The tools we cover here are Ecasound and JACK. The
Hydrogen drum machine is mentioned briefly too. We use no ALSA- or
OSS-specific features directly, and either will do fine. In
fact, for those who have lost their way and have strayed from the path
to enlightenment (kidding), these tools and techniques also work under
CoreAudio on Mac OS X.

Figure 1 shows how data flows between each of these components at
a high level.

Figure 1. Audio Data Flow

Equipment list

For the examples outlined in this article, any sound card will do. I
even have performed some relatively acceptable recordings using the
onboard Intel i8x0 sound device in one of my Linux laptops. However,
the difference between lower-end audio controllers and the mid- to high-end ones is quite noticeable.

We also require a Linux distribution. If you have trouble
getting JACK and Ecasound for your distribution, try the AGNULA live
distribution. Most distributions come with the relevant packages these
days anyway.

A mixer is desirable. Using a small (read: cheap) mixer may give you
more flexibility and a chance at better sound. You also may find that
a direct injection box or a microphone preamp is adequate.

Figure 2. Equipment Signal Flow

Note that Figure 2 suggests plugging the headphones in to your
Linux box. Most mixers allow the sound card to be plugged in to a
signal return port and allow the headphones to receive the audio signal
either before or after the signal is sent to the Linux box. This is
acceptable too.

Assumed Knowledge

In this article, we don't assume much, apart from needing the following:

A Linux box with a configured and tested audio controller.

The ability to source and install necessary packages and their
dependencies.

A familiarity with your choice of noise-making device (for example, guitar, cello,
cat and so on).

Starting jackd

JACK, which stands for the JACK Audio Connection Kit, is an API and
a service that provides audio connectivity between applications on
many POSIX-compliant systems. JACK has been designed with low-latency
communication in mind.

Many of the examples in this article may work equally well without
JACK. I personally have had fewer audio dropouts on systems employing
JACK running with real-time priority than without, and it is quite useful
for interconnecting audio applications, such as the Ecasound and Hydrogen
examples discussed later.

For applications to make use of JACK, they must be linked against
the JACK API libraries, and the JACK service, called jackd, must
be started. Distributions shipped with JACK often already have most
applications linked against the JACK API. If not, consult the build or
compile instructions for your given application.

To start the JACK service, execute a command similar to the
following:

jackd -R -d alsa

The -R option instructs JACK to attempt to attain real-time privilege,
and -d alsa instructs JACK to use the ALSA sound system. For
users still using the OSS sound system, -d oss should suffice, and
-d coreaudio should get Mac OS X users off to a start.

Each driver supports a series of driver-specific options. These may be
viewed by specifying --help after -d alsa.

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